Box hole drill steel

ABSTRACT

Box hole drill steel comprises pipe of short length, i.e. of the order of one yard, to be easily handled with its axis transverse to a mine drift, and of large circumference, i.e. larger than its length, to provide stiffness for straight boring and to transmit large torque for boring a big hole, e.g. 5 feet in diameter, the pipe including a plain carbon steel body with alloy steel pin and box threaded tool joints welded to its ends, each thread being straight (untapered) to minimize hoop tension and being of modified buttress configuration for strength, the thread having a steep pitch and a double lead, being of less than 360* circumference but greater than 180* to insure a tight and stable connection, the pin being provided with a shoulder to engage the box mouth to transmit torque and axial compressive force for turning and loading the bit, the body of the pipe having a handling tube at each end extending diametrically therethrough and welded to the body at each end, the tube providing means by which the pipe can be engaged for lifting, lowering, turning and holding.

Kloesel, Jr. et al.

Nov. 4, 1975 BOX HOLE DRILL STEEL Primary ExaminerWerner H. Schroeder Inventors: Joseph A. Kloesel, Jr.; Otis Ned Assistant E'mminer Moshe Cohan Rodgers, both of Midland Tex Attorne Agent, or FzrmMurray obmson [73] Assignee: Smith International, Inc., Midland,

T [57] ABSTRACT [22] Filed: June 14, 1974 Box hole drill steel comprises pipe of short length, i.e. of the order of one yard, to be easily handled with its [21] Appl. No.. 479,270 axis transverse to a mine drift, and of large circumference, i.e. larger than its length, to provide stiffness for [52] US. Cl. 285/39; /46; /85; raight boring and to transmit large torque for boring 285/1 15; 285/334; 285/390; 285/401; a big hole, e.g. 5 feet in diameter, the pipe including 21 403/19; 403/343 plain carbon steel body with alloy steel pin and box 51 Int. c1. F16L 55/00 threaded tool joints welded to its ends. each thread [58] Field of Search 285/390, 39, 333, 334, being straight (untapered) to minimize hoop tension 285/376, 401, 360, 391; 166/775; 175/52, and being of modified buttress configuration for 53, 85; 403/16, 19, 296, 306, 343, 361; 85/46 strength, the thread having a steep pitch and a double lead, being of less than 360 circumference but greater [56] Refere Cited than 180 to insure a tight and stable connection, the UNITED STATES PATENTS pin being provided with a shoulder to engage .the box mouth to transmit torque and axial compressive force 2,636,753 4/1953 Griffin 285/334 X 2,849,212 8/1958 Robbins 175/85 for .tummg loadmg the the body 9 3,355,192 11/1967 KlOeSel, Jr. et al. 285/334 )4 havng handlmg tube at each end extendmg 3,399,738 9/1968 Haspert 175/53 rically thetethrough and welded to the y at each 3,442,536 5/1969 Fowler 285/376 x the tube Providing means y which the p p can be engaged for lifting, lowering, turning and holding.

6/ 7 M 4 Claims, 7 Drawing Figures a 6 5 6 F 7 m 35 f 1. w

U I I i .13

US. Patent Nov. 4, 1975 Sheet 10m 3,917,319

BOX HOLE DRILL STEEL CROSS REFERENCE TO RELATED PATENTS AND PUBLICATIONS:

A related application also entitled Box Hole Drill Steel is being filed concurrently herewith, assigned to the same assignee as the present application.

The disclosures of the following US. Pat. Nos. and the aforementioned concurrent application are incorporated herein by reference:

3355192 Kloesel, et al; 3754609 Garrett; 3067563 McCool; 2636753 Griffin; 3399738 I-Iaspert; Subterranean Model UR-60 Box Hole Machine, a brochure published by Subterranean Tools, Inc.

BACKGROUND OF THE INVENTION:

This invention relates to drill steel and more particularly to box hole drill steel and connections therefor.

Heretofore it has been known to use flanged couplings for connecting lengths of box hole drill steel. This makes connection and disconnection of the lengths of drill steel a tedious time consuming process.

Possible difficulties with conventional threaded pipe connections if used for box hole drill pipe would be excessive hoop tension due to thread taper when the connection is made up tight enough to prevent accidental loosening, difficulty in applying wrenches for screwing the connections together due to limited space, undue length of connection compared to pipe length, and time required for making several revolutions of the pipe during make up and break out.

Some of the foregoing difficulties have been met in connections for other types of pipe. For example relative to fast make up and break out US. Pat. No. 3442536 to Fowler describes wellhead apparatus including a breech block type connection employing no lead teeth. The references cited in the Fowler patent disclose fast make up interrupted thread type connections. A threaded rotary shouldered connection having rugged modified buttress threads with double lead and a steep pitch for fast make up and break out suitable for use in mine raise drilling is disclosed in US. Pat. No. 3355192 to Kloesel, et al. The theory of rotary shouldered connections for oil well drill pipe is explained at some length in US. Pat. No. 3,754,609 to Garrett. The use of straight threads in conjunction with a torque transmitting shoulder is disclosed in US. Pat. Nos. 2,636,753 and 2,825,585 to Griffin, the connection being between a length of drill pipe or a drill collar and a tool joint replaceably shrink fitted thereto. Tubular drill rod for blast hole drilling having threaded ends and provided adjacent each end with a transverse sleeved hole for reception of a holding bar is shown in US. Pat. No. 2,849,212 to Robbins. Guide pipe for a box hole drill, the pipe having transverse holes but without sleeves therein is shown in US. Pat. No. 3,399,738 to Haspert.

Some idea of the practical differences between the foregoing prior art constructions and the present invention will appear when it is noted that ordinary oil field drill pipe is usually of the order of 30 feet long and a foot or two in circumference for downwardly drilling 5000 foot deep holes of less than a foot in diameter, blast hole drill rod is similar to oil field drill pipe but usually somewhat shorter, e.g. 20 feet in length and used to drill downwardly a hole of about a foot in diameter and of a 100 feet or less in depth, raise drill steel is used to drill, usually upwardly from above through a pilot hole, a raise or tunnel of perhaps feet in length and of the order of 3 to 15 feet in diameter, the steel itself having a circumference of a couple of feet and a length of 10 feet or so, whereas box hole drill steel to which the present invention pertains is used in drilling upwardly from below and without a pilot hole an inclined passage of about 5 feet in diameter and perhaps 30 feet long, the length of the steel being of the order of one yard and having a large circumference, i.e. larger than its length. The foregoing is summarized in the following table of typical dimensions:

Different utilities create different combinations of requirements to be met and problems to be overcome; the present construction meets the requirements of box hole drilling and advantageously overcomes the problems of prior box hole steel constructions discussed above. Other objects and advantages of the invention will appear from the following description.

SUMMARY OF THE INVENTION According to the invention box hole steel comprises pipe of short length, ie of the order of one yard or so, and having a circumference to length ratio greater than one, the ends each being provided with a rotary shouldered tool joint having straight, modified buttress, double lead, high pitch threads of less than 360 but greater than 180 circumferential extent, i.e. the circumferential extent of each thread is of the same order as the length of the pipe body to which the tool joints are connected and greater than the arc subtended by, e.g., the length of the adjacent bar receiving tube, the extent preferably being 270. Holding means are provided for supporting a string of the pipe in the hole against axial movement while pipe lengths are being added or removed and to prevent rotation of the pipe relative to the hole or the drilling head when making and breaking connections. The present application is one of two related applications in one of which (the present application) the holding means includes a bar receiving tube transecting the pipe near one or preferably both ends and such holding means forms part of the invention, such holding means not being claimed in the other application.

BRIEF DESCRIPTION OF DRAWINGS For a detailed description of a preferred embodiment of the invention, reference will now be made to the accompanying drawings wherein:

FIG. 1 is a schematic sectional view of a gold mine with a box hole drill operating therein employed box hole drill steel in accordance with the invention;

FIG. 2 is a sectional view of a length of box hole drill steel embodying the invention;

FIG. 3 is a schematic isometric view of the tool joint threads in accordance with the invention;

FIG. 4 is a sectional view showing the details of the pin tool joint of the drill steel in accordance with the invention;

FIG. 5 is a sectional view showing the thread form of the pin tool joint of the drill steel in accordance with the invention;

FIG. 6 is a sectional view showing the details of the box tool joint of the drill steel in accordance with the invention; and

FIG. 7 is a sectional view showing the thread form of the box tool joint of the drill steel in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there is shown a mine drift 11 in which is disposed a drill 13. A drill string 15 extends into box hole 17 which, as indicated by the broken lines, will ultimately extend up to a drift, sublead, stope or box 19 in which a man will mine gold. The drill string includes a plurality of lengths of drill steel 23. Certain pieces of drill steel may have on their exteriors various structures such as the wall engaging means of stability 25, the detritus diverter or shield 27, and the multiple cutters of bit 29. The term drill steel as used herein is intended to cover all drill string elements employing drill steel in accordance with the invention regardless of whether or not combined with such other structure. It is also to be noted that the last element of the drill string, namely the drill bit, embodies the invention at only one end, the other end being adapted for contacting the end of the hole rather than for connection to other drill steel, but to a certain extent the bit body may incorporate the present invention.

The above described apparatus is operated to drill a box hole by rotating the drill string with the drill l3 and advancing the bit in the hole to maintain pressure against the end of the hole. The detritus falling away from the bit drops down the inclined hole 17 and into trough 30 and then into the drift for ultimate disposal.

Referring now to FIG. 2, there is shown one of the lengths of drill steel 23 included in the drill string 15. Steel 23 includes a tubular body 31 of plain carbon steel, having pin and box alloy steel tool joints 33, 35

welded to its ends. For a discussion of the merits of alloy steel tool joints see U.S.' Pat. No. 3,067,563 to M. G. McCool.

. The body 31 typically has a thickness of /2 inch. Other typical dimensions of thedrill steel would be as shown in the following table:

External Overall Ratio of Outside Length Circumference Circumference Diameter in Inches in Inches to Length l3 24(to 36) 4l l.7(tol.l5) 14% 36 46 L3 48 63 [.3

4 cally the tubes are made of steel and have an inner diameter of about three inches, large enough to receive holding rods, and a wall thickness of inches, strong enough to transmit the required forces and torques between the drill steel and holding rod. In connection with some drilling machines only one holding tube may be necessary for making, breaking, and supporting the drill steel in the drill string, but two are preferred in any case because. these tubes provide transverse structural support for the large circumference pipes. Each holding tube 35 extends through radial holes 37 in the body 31,.being welded at each end to body 31 by annular welds 39 extending around the tube ends between the tube and the outside of the body. If desired additional annular welds between the tube and inside of the body may be used. The tubes are adapted to receive holding rods extending therethrough and through the frame of drilling machine or drill 13 (FIG. 1), eg to support the drill string axially and against rotation when the lowermost piece of drill steel, adjacent the drill, is being inserted and connected or disconnected and removed. One or more holding rods can also be used to lock the lowermost drill steel to the drill head or to anchor it to the drill frame in the course of such operations, as will be described in more detail hereinafter. The drill steel 1 is thus adapted for use in a drilling machine of the type disclosed in the above referenced brochure of Subterranean, modified to use threaded connections, as shown in FIG. 1, although the steel could be used with other similar drills or drilling machines. The steel is not intended to carry drilling fluid but it is understood that users, not the present inventors, have added a small internal pipe to convey water to the bit for dust suppresslon.

Turning now to the tool joints 33, 35, each includes a short weld neck 51 of the same inner and outer diameter as body 31 adapted for welding to the body 31 by annular welds 53. Pin tool joint 33 further includes an exteriorly threaded pin 55 of smaller outer diameter than body 31 and a transition zone 57. The outer end of the transition zone provides an annular shoulder 59 for engagement with the end shoulder of another length of drill steel, similar to end shoulder 61 on the box tool joint 35. The box tool joint 35 further includes an interiorly threaded box 63 adapted to engage with the pin of another tool joint like pin 55 of pin tool joint 33. The outer diameter of box 63 is the same as that of body 31 and the wall thickness is greater than that of the body 31, being about /8 inch exclusive of the thread. The pin 55 is only slightly thicker, being about inch exclusive of the thread (see FIG. 4).

The pin and box tool joints are untapered and are provided with threaded portions 65, 67. The threads are helical and of modified buttress configuration with. 45 unengaged flank angles and l5 pressure flanks. The threads are double lead, that is, there are two pin threads 65A, 65B and two box threads 67A, 673, the turns of one thread at each end lying in between the turns of the other thread at that end. The thread lead is l inch (two threads per inch double lead) and since the threaded portions of the pin and box extend axially only one inch, there is room for but one turn of each thread. The ends of each turn would be imperfect and such portions are removed leaving only about A1 turn or a circumferential extent of about 270. This leavesa gap of about or turn. Since the threads are dou ble. the corresponding ends of the threads are displaced 180. This results in the 90 gap in one thread having the same azimuthal position as the mid-part of the adjacent thread. This provides stability and prevents one length of pipe from canting relative to the adjacent length of pipe even though the axial length of the threaded portions 1 inch) is less than of the outer diameter of the pipe. The relative positions of the threads at each end of the pipe are exemplified in FIG. 3.

Dimensional details and tolerance for the pin and box tool joints and threads preferred for a box hole drill steel of 14% inch diameter are shown in FIGS. 4-7. Comparing FIGS. 4 and 6 it will be noted that the pin thread crest diameter is less than the box thread valley diameter so that the pin thread crests do not engage the box thread valleys. Likewise, the diameter of the pin thread valley is less than the diameter of the box thread crests so that the box thread crests do not engage the pin thread valleys. This clearance is characteristic of a straight thread since without a taper there is no way to expand the box over the pin as would be required if '7 the aforementioned Kloesel et al US. Pat. No. 3,355,197, as follows:

Pressure Flank Angle: 10 to degrees Unengaged Flank Angle: Lead: Taper:

to 60 degrees V4 to 1% Zero 1 A" per foot The threads are quite coarse for ruggedness, but if a somewhat finer thread were used, higher thread multiplicity than two could be used without the lead becoming excessive.

Referring now particularly to FIG. 2, the pin tool joint has an annular unthreaded portion 71 between the shoulder 59 and the threaded portion 65. Also the box tool joint has an unthreaded portion 73 between the end shoulder 61 and threaded portion 67. These unthreaded portions are respectively stretched and compressed when the tool joints are made up tighter after the shoulder 59 of a pin joint engages the mouth 61 of a box joint. The resultant frictional engagement of the shoulders 59 and 61 is sufficient to transmit all or most of the torque between the pin and box tool joints without the threads being subjected to torque. The connection is therefore a rotary shouldered connection.

To effect torque transmission through the shoulder of a rotary shouldered connection, as is intended, the connection must be made up tight enough to create the necessary axial compression of the unthreaded portion or pin neck 71 and the unthreaded portion or box mouth 73. For example in the illustrated embodiment a make up torque of 40,000 foot pounds is suitable. To insure that the drill string can be broken apart as is necessary to remove it from the box hole, break out torque should be less than makeup torque. The connection of the present invention meets this requirement with a breakout torque at 36,000 foot pounds when made up with 40,000 foot pounds. Break out torque is thus only 90% of make up torque.

Reference will now be made once more to FIG. 1 to describe the operations performed when pipe lengths are to be added to the drill string for continuing forward drilling and when pipe lengths are to be removed 6 from the drill string when the bit is to be retracted from the hole, e.g. when drilling has been completed or when the drill bit or a cutter thereof is to be replaced. it is to he understood that in the preferred method of use the drill pipe is run in the hole with the box up and pin down.

If it is desired to add a joint of pipe. the machine being at the upper limit of its travel, the lower holding tube of the lowermost joint in the string is pinned to the drilling machines frame with a bar 81. The machine is operated in reverse to completely unscrew the machine head box 82 from the pin of the lowermost joint. The machine head is then retracted to its lowermost position. Handling arm 83 loaded with another pipe joint swings the additional joint into position between the head box and the pin at the lower end of the drill string. The head is raised and rotated to screw the head box to the pin of the added pipe joint and to screw the box of the added pipe joint to the pin at the lower end of the drill string. The rod 81 is then removed and drilling can proceed.

When it is desired to remove the drill string from the hole. this is accomplished one joint at a time as follows. With the head at its upper limit of travel the lower holding tube of the lowermost joint in the string is pinned to the machine frame with bar 81. The machine is then operated in reverse to partially unscrew the head box from the drill string pin. The bar 81 is then removed and the head retracted to its lowermost position, the drill string lowering also. The head is then pinned to the lower holding tube of the lowermost joint of pipe and the upper holding tube of the next to lowest joint of pipe is pinned to the machine frame with bar 81. The machine is operated in reverse to unscrew the lowermost joints box from the pin of the next to lowermost joint. The handling arm 83 is then moved into position around and gripping the lowermost joint of pipe. The machine is then operated in reverse to unscrew the lowermost joint of pipe which is held against rotation by the handling arm. The handling arm and the lowermost joint are then moved away and the head elevated and loosely screwed onto the lowermost pin of the remaining portion of the drill string. The bar 81 is removed and the drill string lowered to the lowermost position of the machine. The procedure is repeated until all of the desired portions of the drill string have been removed.

A feature of the invention is the fact that because of the thread configuration, less than one revolution of the drilling machine is required for make up and break out of pipe joints.

As previously mentioned one of the problems encountered in box hole drilling is the limited space available. The drilling apparatus, including both the drilling machine or drill and the drill pipe must have a maximum extent sufficiently short to enable it to go down the mine shaft in the elevator cage, then along the low ceilinged horizontal drift. go through pressure doors, around bends, and along rails. Blasting disturbs the walls of the mine shaft and drifts are made as small as practicable. It is for these reasons that the box hole pipe is short, e.g. of the order of 1 yard plus or minus 50%. During drilling the drill string is at an angle and tends to bend over. To keep the string as straight as possible it must be stiff. Stiffness varies with the fourth power of the circumference, so a large circumference pipe is desirable. It is the combined result of these two requirements that result in the pipe having a circumference to length ratio greater than unity as previously set 7 forth.

During drilling the drill string is in compression. Axial compression is transmitted by the shoulders of the rotary shouldered connection, rather than through the threads, and, as previously explained, torque is also transmitted through the shoulders. Therefor the threads do not take the drilling loads. This facilitates use of the 270 threads. It is also to be noted that the use of a double lead provides thread support on the entire 360 even though each thread is only 270 in extent. Finally, as explained in the foregoing Griffin patent, only the end turns of a thread take much of the axial load. For these reasons there is adequate thread strength provided by the fast make up thread of the present invention.

While a preferred embodiment of the invention has been shown and described, modification thereof can be made by one skilled in the art without departing from the spirit of the invention.

We claim:

1. Box hole drill steel comprising a tubular body having rotary shouldered connections at its ends and holding tubes extending transversely across the body adjacent to its ends, said connections including multiple lead modified buttress threads of less than 360 extend and having a break out torque less than make up torque, the steel having a length of the order of 1 yard plus or minus 50 percent with a circumference to length ratio greater than unity.

2. Box hole drill steel according to claim 1 said threads being provided with a pressure flank angle between 10 and 20 and an unengaged flank angle between 30 and 60 and a lead of between inch and 1%, inches, a taper of zero plus or minus /2 inch per foot, and a circumferential extend of less than 360.

3. Steel according to claim 2 in which said pressure and disengaged flank angles are respectively 15 and 45, said ratio is about 1.3, said circumferential extent is about 270, and said lead is 1 inch, in each case plus or minus 10 percent, and the taper is substantially zero,

said holding tubes extending diametrically across said 1 body.

4. Box hole drill steel according to claim 1 wherein said threads are helical and of double lead each of less than 360 extent leaving a gap in each thread with respect to its extending all around the circumference of the steel, the gaps in said threads being disposed 180 apart.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3 I917 I319 DATED i November 4, 1975 INVENTO I Joseph A. Kloesel, Jr. Otis Ned Rodgers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 24, change "stability" to -stabilizer.

Column 3, 1'. 1 e 67, change "Transacting" to --Transecting.

Column 5, in the table of dimensions, change "3/4' to ll/4"'to 3/4" to ll/l4"--.

Column 7, line 6, change "therefor" to -therefore-.

Column 5, line 27, change "5555197" to -5555192.

Signed and Sealed this Seventeenth D3) 0f August 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL D-ANN Allesling Office Commissioner ofParents and Trademarks 

1. Box hole drill steel comprising a tubular body having rotary shouldered connections at its ends and holding tubes extending transversely across the body adjacent to its ends, said connections including multiple lead modified buttress threads of less than 360* extend and having a break out torque less than make up torque, the steel having a length of the order of 1 yard plus or minus 50 percent with a circumference to length ratio greater than unity.
 2. Box hole drill steel according to claim 1 said threads being provided with a pressure flank angle between 10* and 20* and an unengaged flank angle between 30* and 60* and a lead of between 3/4 inch and 1 1/4 inches, a taper of zero plus or minus 1/2 inch per foot, and a circumferential extend of less than 360*.
 3. Steel according to claim 2 in which said pressure and disengaged flank angles are respectively 15* and 45*, said ratio is about 1.3, said circumferential extent is about 270*, and said lead is 1 inch, in each case plus or minus 10 percent, and the taper is substantially zero, said holding tubes extending diametrically across said body.
 4. Box hole drill steel according to claim 1 wherein said threads are helical and of double lead each of less than 360* extent leaving a gap in each thread with respect to its extending all around the circumference of the steel, the gaps in said threads being disposed 180* apart. 